Presently, aluminum metal is flash evaporated on the inside surfaces of a large screen projection system and more particularly on the inside surfaces of a "PRT" projection ray tube, in which the image is projected on opposite sides of the screen, using a tungsten wire filament having an aluminum pellet mounted on an open end of the tungsten wire filament. The PRT is placed over the tungsten filament and vacuum sealed prior to alumination. The tungsten filament is then heated to heat the aluminum pellet until flashing occurs. A projection ray tube is manufactured with a very small size diameter neck generally limited to about 24 mm. Because the neck is so small in size other known type of resistance heated flash evaporators including the resistance heated flash evaporator vessel or "flash evaporator vaporization boat", as it is sometimes referred to, are not currently useable as a substitute for the tungsten wire filament.
The conventional flash evaporator vessel or vaporization boat is a structure composed of intermetallic composite materials such as titanium diboride and boron nitride or a composite of titanium diboride, boron nitride and aluminum nitride. Alternatively the structure may be formed from a graphite body. The conventional flash evaporator vessel has a geometry preferably of rectangular configuration in which a cavity is machined to receive the metal charge to be vaporized. Ordinarily the flash evaporator vessel is placed in a vacuum chamber adjacent to the surface of the object to be coated and is connected at its opposite ends through a clamp to an external source of electrical power. Flashing of the metal charge requires good contact to be made to the clamp and equally important the current density generated in the evaporator vessel must be high enough to cause a sufficient hot zone to form across the cavity which will raise the metal charge in the cavity to its vaporization temperature.
For use in connection with a projection ray tube the flash evaporator vessel must be sized to fit inside the open neck of the PRT tube and provide sufficient current density to flash the metal charge. In addition the flash evaporator vessel should be configured to permit automatic pellet insertion into the vessel on an assembly line basis so that the same flash evaporator can be used repeatedly and reliably.